Anytime I look at guns at a pawnshop, I always ask if they have anything in the back thats broken or doesn't function right. You will be surprised at what you can find. Also look for advertised Gunsmith Specials from online retailers (royal tiger, centerfire, classic firearms, old western...
Had the same issue with my AR40 and my dads AR9. Installed this feed ramp and they both work fine now.
https://taccom3g.com/product/taccom-glock-lower-feedramp/